Optimize public schedule speaker queries

backend/api/schedule/tests/test_schedule_frontend_query.py

@@ -0,0 +1,218 @@
+from datetime import date, time
+
+import pytest
+
+from conferences.tests.factories import (
+    AudienceLevelFactory,
+    ConferenceFactory,
+    DurationFactory,
+    KeynoteFactory,
+    KeynoteSpeakerFactory,
+)
+from files_upload.tests.factories import ParticipantAvatarFileFactory
+from participants.tests.factories import ParticipantFactory
+from schedule.models import DayRoomThroughModel
+from schedule.tests.factories import (
+    DayFactory,
+    RoomFactory,
+    ScheduleItemAdditionalSpeakerFactory,
+    ScheduleItemFactory,
+    SlotFactory,
+)
+from submissions.tests.factories import SubmissionFactory, SubmissionTypeFactory
+
+SCHEDULE_QUERY = """
+query Schedule($code: String!, $language: String!) {
+  conference(code: $code) {
+    id
+    timezone
+    days {
+      day
+      rooms {
+        id
+        name
+        type
+      }
+      slots {
+        id
+        hour
+        endHour
+        duration
+        type
+        items {
+          id
+          title
+          slug
+          type
+          duration
+          hasLimitedCapacity
+          userHasSpot
+          hasSpacesLeft
+          spacesLeft
+          linkTo
+          audienceLevel {
+            id
+            name
+          }
+          language {
+            id
+            name
+            code
+          }
+          submission {
+            id
+            title(language: $language)
+            duration {
+              id
+              duration
+            }
+            audienceLevel {
+              id
+              name
+            }
+            speaker {
+              id
+              fullName
+            }
+            type {
+              id
+              name
+            }
+            tags {
+              id
+              name
+            }
+          }
+          keynote {
+            id
+            title(language: "en")
+            slug(language: "en")
+            speakers {
+              id
+              fullName
+            }
+          }
+          speakers {
+            id
+            fullname
+            participant {
+              id
+              photo
+            }
+          }
+          rooms {
+            id
+            name
+            type
+          }
+        }
+      }
+    }
+    audienceLevels {
+      id
+      name
+    }
+    durations {
+      id
+      duration
+      allowedSubmissionTypes {
+        name
+      }
+    }
+  }
+}
+"""
+
+
+@pytest.mark.parametrize("item_count", [1, 4])
+@pytest.mark.parametrize(
+    ("item_source", "expected_queries"),
+    [("submission", 13), ("keynote", 14), ("additional", 13)],
+)
+@pytest.mark.django_db
+def test_frontend_schedule_query_is_constant(
+    graphql_client,
+    django_assert_num_queries,
+    item_count,
+    item_source,
+    expected_queries,
+):
+    conference = ConferenceFactory()
+    day = DayFactory(conference=conference, day=date(2026, 5, 29))
+    room = RoomFactory(name="Main room")
+    DayRoomThroughModel.objects.create(day=day, room=room)
+
+    audience_level = AudienceLevelFactory()
+    conference.audience_levels.add(audience_level)
+    submission_type = SubmissionTypeFactory()
+    conference.submission_types.add(submission_type)
+    duration = DurationFactory(conference=conference, duration=30)
+    duration.allowed_submission_types.add(submission_type)
+
+    for index in range(item_count):
+        slot = SlotFactory(day=day, hour=time(9 + index), duration=30)
+        if item_source == "submission":
+            submission = SubmissionFactory(
+                conference=conference,
+                audience_level=audience_level,
+                duration=duration,
+                type=submission_type,
+                status="accepted",
+                tags=[f"tag-{index}"],
+            )
+            speaker = submission.speaker
+            ScheduleItemFactory(
+                conference=conference,
+                slot=slot,
+                submission=submission,
+                type="submission",
+                rooms=[room],
+                language="en",
+            )
+        elif item_source == "keynote":
+            keynote = KeynoteFactory(conference=conference)
+            keynote_speaker = KeynoteSpeakerFactory(keynote=keynote)
+            speaker = keynote_speaker.user
+            ScheduleItemFactory(
+                conference=conference,
+                slot=slot,
+                submission=None,
+                keynote=keynote,
+                type="keynote",
+                rooms=[room],
+                language="en",
+            )
+        else:
+            schedule_item = ScheduleItemFactory(
+                conference=conference,
+                slot=slot,
+                submission=None,
+                type="custom",
+                rooms=[room],
+                language="en",
+            )
+            additional_speaker = ScheduleItemAdditionalSpeakerFactory(
+                scheduleitem=schedule_item
+            )
+            speaker = additional_speaker.user
+
+        ParticipantFactory(
+            conference=conference,
+            user=speaker,
+            photo_file=ParticipantAvatarFileFactory(uploaded_by=speaker),
+        )
+
+    with django_assert_num_queries(expected_queries):
+        response = graphql_client.query(
+            SCHEDULE_QUERY,
+            variables={"code": conference.code, "language": "en"},
+        )
+
+    assert "errors" not in response
+    items = [
+        item
+        for slot in response["data"]["conference"]["days"][0]["slots"]
+        for item in slot["items"]
+    ]
+    assert len(items) == item_count
+    assert all(item["speakers"][0]["participant"]["photo"] for item in items)

backend/api/schedule/types/schedule_item.py

@@ -4,6 +4,7 @@
 import strawberry
 import strawberry_django
 from django.db import models as django_models
+from django.db.models import Prefetch
 from django.db.models.functions import Coalesce
 
 from api.context import Info
@@ -12,6 +13,7 @@
 from api.schedule.types.room import Room
 from api.schedule.types.schedule_item_user import ScheduleItemUser
 from api.submissions.types import Submission
+from participants import models as participant_models
 from schedule import models
 
 if TYPE_CHECKING:  # pragma: no cover
@@ -163,13 +165,30 @@ def user_is_talk_manager(self, info: Info) -> bool:
 
         return self.talk_manager_id == user_id
 
+    # ScheduleItemUser is a DTO, so Strawberry Django cannot propagate the
+    # Participant.photo optimization through it to these reverse relations.
     @strawberry_django.field(
         only=["conference_id"],
         select_related=["submission__speaker"],
         prefetch_related=[
-            "submission__speaker__participants",
-            "keynote__speakers__user__participants",
-            "additional_speakers__user__participants",
+            Prefetch(
+                "submission__speaker__participants",
+                queryset=participant_models.Participant.objects.select_related(
+                    "photo_file"
+                ),
+            ),
+            Prefetch(
+                "keynote__speakers__user__participants",
+                queryset=participant_models.Participant.objects.select_related(
+                    "photo_file"
+                ),
+            ),
+            Prefetch(
+                "additional_speakers__user__participants",
+                queryset=participant_models.Participant.objects.select_related(
+                    "photo_file"
+                ),
+            ),
         ],
     )
     def speakers(self) -> list[ScheduleItemUser]: